Note: Descriptions are shown in the official language in which they were submitted.
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THIN POLYSTYRENE FILMS
CONTAINING POST-CONSUMER RECYCLED POLYSTYRENE
This invention relates to thin, substantially clear,
oriented polystyrene ~ilms cont~;n;ng post-consumer recycled
polystyrene. More speci~ically, this invention relates to such
~ilms that can be use~ul as window envelope ~ilms.
A window envelope is an envelope with one or more openings
o~ any shape, usually rectangular, which allows examination o~
any in~ormation, typically a name and an address, printed on a
limited area o~ matter within the envelope. The opening or
openings in the envelope are sealed or closed by a window patch
composed o~ a substantially clear ~ilm, typically polystyren-e.
Patching is the process in which window envelope ~ilm is cut
into patches o~ a desired length and width, and applied to the
window envelope.
Window envelope ~ilms are typically composed primarily o~
extruded polystyrene and, optionally, contain a small proportion
o~ a rubber-modi~ied polymer, such as high-impact polystyrene
("HIPS ), to add a cosmetically desirable haze or measure o~
translucency to the ~ilm. Window envelope ~ilm may be
manu~actured in biaxial or uniaxial orientations. Biaxial
orientation is generally pre~erred because of the superior
cutability o~ the ~ilm in the transverse or cross machine
direction.
For environmental reasons, it has become increasingly
important to reduce the volume of plastics which are land~illed.
To reduce this volume o~ land~illed plastics, many e~orts have
been made to utilize post-consumer recycled plastic in various
products. However, e~orts to utilize post-consumer recycled
polystyrene in thin, substantially clear, oriented polystyrene
~ilms has proven di~icult. Accordingly, there still exists a
need in industry to utilize post-consumer recycled polystyrene
in thin, substantially clear, oriented polystyrene ~ilms,
including window envelope ~ilms.
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The present invention provides thin, substantially clear,
oriented polystyrene ~ilms cont~;n;ng post-consumer recycled
polystyrene and possessing physical properties substantially
similar to that o~ polystyrene ~ilms not cont~;n;ng post-
consumer recycled polystyrene. Films o~ the present inventionmay comprise up to 100 percent post-consumer recycled
polystyrene.
Films o~ the present invention are generally at least
about 0.25 mils (6.35 microns), and pre~erably at least about
0.75 mils (19.05 microns) thick. Films o~ the present invention
are generally not more than about 7 mils (177.8 microns),
pre~erably not more than about 4 mils (101.6 microns), and more
pre~erably not more than about 2.5 mils (63.5 microns) thick.
Films o~ the present invention are either uniaxially or
biaxially oriented. Pre~erably, ~ilms o~ the present invention
are biaxially oriented.
Films o~ the present invention generally are composed
primarily o~ extruded polystyrene. The ~ilms may contain small
amounts o~ an anti~lecking agent and an acid scavenger such as
taught in U.S. Patent Nos. 5,009,953 and 5,190,814. The ~ilms
may also contain a small proportion o~ a hazing agent, such as
high-impact polystyrene ("HIPS") ~or example, to add a
cosmetically desirable haze or measure o~ translucency to the
~ilm. A pre~erred HIPS use~ul as a hazing agent is STYRON 404
(available ~rom The Dow Chemical Company).
The extruded polystyrene use~ul in making ~ilms o~ the
present invention may contain up to 100 percent by weight o~
post-consumer recycled polystyrene. The post-consumer recycled
polystyrene meets the de~inition o~ post-consumer materials
given in ASTM D5033-90. The extruded polystyrene use~ul in the
present invention may also contain general purpose polystyrene.
The particular general purpose polystyrene is not especially
critical. However, one pre~erred general purpose polystyrene is
STYRON 665 (available ~rom The Dow Chemical Company). The
extruded polystyrene use~ul in the present invention may also
contain in-plant scrap ~rom ~ilms o~ the present invention.
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Typically, the extruded polystyrene is a blend of general
purpose polystyrene, scrap from films of the present invention,
and post-consumer recycled polystyrene.
The post-consumer recycled polystyrene useful in the
present invention must be substantially ~ree of particulates
such as paper fibers, rubber bands, and crosslinked gels in
order to prevent agglomerates or holes in the film upon
orientation. A Soxhlet extraction technique was used to test
the amounts of particulates in various samples of post-consumer
recycled polystyrene. This Soxhlet extraction technique used a
10 micron filtration process with toluene as the solvent. Using
the Soxhlet extraction, each sample of post-consumer recycled
polystyrene was weighed and then dissolved in toluene. The
dissolved sample was filtered using the lO micron filtration
process and any nonsoluble solid particulates recovered by the
~iltration process was weighed. The weight of the filtered
particulates was divided by the weight o~ the original sample to
det~m; n~ the weight percent of particulates in the original
sample. Generally, post-consumer recycled polystyrene useful in
the present invention should have less than about 0.1 percent by
weight particulates as measured by this Soxhlet extraction
technique. Pre~erably, the post-consumer recycled polystyrene
will contain no detectable amount o~ particulates as measured
via this Soxhlet extraction technique.
The post-consumer recycled polystyrene must also be
substantially free o~ contAm;n~tion with other types of polymers
such as polypropylene and polyethylene in order to avoid melt
incompatibility. Melt incompatibility can result in a mottled
film surface. Preferably, the post-consumer recycled
polystyrene materials would indicate only one glass transition
temperature at about 100~C when analyzed via digital s~nn;n~
calorimetry using the method cited in ASTM D-3418.
The post-consumer recycled polystyrene should be
substantially clear in order to produce good optical clarity in
the resulting ~ilm. The post-consumer recycled polystyrene must
be substantially ~ree of inks, food oils, and other pigmented
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cont~m;n~nts. Pla~ues made from post-consumer recycled
polystyrene pressed on a platen press at 400~F (204.4~C) to a
thickness of approximately 0.10 ;nch~s (0.254 cm) should have
less than 20 percent haze as measured by ASTM D-1003.
S Preferably, the post-consumer recycled polystyrene useful
in the present invention would be recycled from clear, injection
molded or th~m~formed polystyrene parts. More preferably, the
recycled polystyrene materials would be sourced from compact
disc jewel boxes, compact disc jewel box clear inserts, audio
tape boxes, cookie trays, or berry boxes.
Calcium carbonate is an undesirable cont~m;n~nt sometimes
found in post-consumer recycled polystyrene. Sources of post-
consumer recycled polystyrene cont~;n;ng less calcium carbonate
are preferable for use in the present invention. Although the
upper limit of calcium carbonate acceptable in post-consumer
recycled polystyrene used in the present invention is not
precisely known, post-consumer recycled polystyrene having
amounts of calcium carbonate as high as 575 ppm have been
successfully incorporated into films of the present invention.
The amount of calcium carbonate acceptable may depend on the
percent of post-consumer polystyrene used and the particular
end-use of the film produced. This amount should be
det~m;n~hle without undue experimentation.
Films of the present invention can be made by any
techni~ue known in the art. More specifically, films of the
present invention can be oriented by any techni~ue known in the
art. However, when processing resin cont~;n;ng post-consumer
recycled polystyrene to manufacture films of the present
invention, it may be necessary to make minor adjustments to the
melt temperature in order to maintain the orientation levels one
would get when similarly processing resin cont~;n;n~ no post-
consumer recycled polystyrene. These adjustments generally
result in a decrease of up to about 10~C in melt temperature.
The level of adjustment in melt temperature needed to maintain a
given level of orientation may depend on the source and amount
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o~ post-consumer recycled polystyrene. However, this level o~
adjustment can be det~mined without undue experimentation.
A number o~ post-consumer recycled polystyrene sources
proved di~~icult or impossible to process into thin, oriented
5 ~ilms. For example, resin from recycled ~oamed cups and foam
J sheet food-service container (SP-012 available ~rom Dart
Container Corporation) contained many large gels clearly visible
to the unaided eye. During processing o~ SP-012 significant
extruder surging was observed, apparently due to inconsistent
10 resin pellet size.
Another source o~ post-consumer recycled polystyrene
tested was PC-1000 (available ~rom the National Polystyrene
Recycling Company). PC-1000 is produced from food-service
containers and serviceware (trays and plates). The Soxhlet
lS extraction test showed that PC-1000 contained approximately 1.7
percent by weight o~ particulates.
An attempt was made to process a resin cont~;n;ng 65.75
percent by weight o~ general purpose polystyrene (STYRON-665),
25 percent by weight o~ PC-1000, 8 percent by weight high-impact
polystyrene (STYRON 404), and 1.25 percent CN-201 (available
~rom Polycom Huntsman) into a .2 mil (130.48 micron), biaxially
oriented ~ilm. However, the ~ilm web broke about every 20 to 45
minutes, making it di~icult to collect sam~ples. CN-201 is a
pre-compounded blend o~ 20 percent by weight
polytetra~1uoroethylene, 1 percent by weiyht calcium stearate,
and 79 percent by weight STYRON 665.
The National Polystyrene Recycling Company produces
another source of post-consumer recycled polystyrene: PC-lOOOD.
PC-lOOOD is recycled ~ood-service waste ~rom the Los Angeles
school system. This source o~ post-consumer recycled
polystyrene is lower in cont~m~n~nts than PC-1000 due to tighter
source controls. Analyzed lots of PC-lOOOD showed between O.1
percent and 1.6 percent insolubles via Soxhlet extraction.
An attempt was made to produce a biaxially oriented ~ilm
~rom the resin above except the 25 percent by weight o~ PC-1000
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was replaced with 25 percent by weight of PC-lOOOD. However,
the film web broke approximately every 30 minutes. This is a
clear indication that even cont~m;nAtion levels as low as 0.1
percent (as measured by Soxhlet extraction) present significant
processing problems.
Examples
Five separate biaxially oriented films were produced: a
control sample, two comparative samples, and two examples of the
present invention. The thickness of each ~ilm was. 1.2 mils
(30.48 microns).
The control film contained 95 percent by weight of general
purpose polystyrene (STYRON 665) and 5 percent by weight of
high-impact polystyrene (STYRON 404). Each of the other four
films had enough general purpose polystyrene displaced with
post-consumer recycled polystyrene so that each of the other
four films contained 25 percent by weight of post-consumer
recycled polystyrene.
Comparative Samples ~1 and ~2 respectively contained 25
percent by weight of PC-1000 and PC-lOOOD. Example #1 cont~;ne~
25 percent by weight of PC-4000 (available from the National
Polystyrene Recycling Company). Example #2 contained 25 percent
by weight of PCR-100 (available from Plastic Recycling, Inc.).
The source of the post-consumer recycled polystyrene in
PC-1000 and PC-lOOOD has already been discussed. The source of
post-cansumer recycled polystyrene in PC-4000 is recycled
compact disc jewel boxes and th~rm~formed polystyrene cookie
trays. The source of post-consumer recycled polystyrene in
PCR-100 is recycled compact disc jewel boxes. For both PC-4000
and PCR-100 the amount of particulates present as measured by
the Soxhlet extraction test was too small to be detectable.
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Each of the five films were tested for haze via ASTM
D-1003; 60 degree Gloss, Outside, machine direction; via ASTM
D-2457; ultimate tensile, machine direction, via ASTM D-882; and
ultimate elongation, machine direction, via ASTM D-882. The
results of these tests are shown in Table I.
J
TABLE I
Control percent percent percent percent
PC-1000 PC-1000 PC-4000 PCR-100
D
Haze (percent)4.56 24.3 9.22 4.41 3.30
60 degree Gloss, 127 84 129 139
(percent)
Ultimate Tensile, 13082 9146 10070 12894 12152
(psi)
Ultimate 45 6.2 4.4 46 51
Elongation,
(percent)
Films of the present invention have been successfully used
as window envelope films. One such window envelope film
contained 49 percent by weight of STYRON 665, 35 percent by
weight PCR-100, 5 percent by weight STYRON 404, and 1~ by weight
CN-201. The film had a thickness of 1.2 mils (30.48 microns).
This film was successfully tested on an F.L. Smithe High Speed
Patcher at 800 patches per minute and 7 inches (17.78 cm) Hg
vacuum for 4000 feet.
Another window envelope film successfully tested contained
35 percent by weight PCR-100, 34 percent by weight STYRON 665,
15 percent by weight in-plant recycled film, 15 percent STYRON
404, 0.8 percent calcium stearate, and 0.2 percent
polytetrafluoroethylene (MP1100 available from DuPont). This
film had a thickness of 1.2 mils (30.48 microns).
i
